The \(\mathcal {C}^{(g)}_{0\ n.a.}\)  reported in eq.(REF ) was earlier computed in Eq.(11) of [1]} and in Eq.(4.9) of [2]}. In order to understand why our result is different with respect to those, let us perform a symbolic analysis of the 1-loop amplitude, in order to understand which terms are contributing.
Within our calculation, we can make series expansions of coefficients
and MIs in the three parameters: \(\epsilon ,s,E\) :
\(c^{(g)}_{i} &=& \sum _{j,k,\ell } c^{(g)}_{i,j,k,l} \, \epsilon ^j s^k E^\ell \ , \\I_i &=& \sum _{j,k,\ell } \mathcal {I}_{i,j,k,l} \, \epsilon ^j s^k E^\ell \ ,\) 
